A new class of soft contact lenses, water gradient silicone hydrogel contact lenses, have been developed and successfully introduced in the market. This new class of silicone hydrogel contact lenses is characterized by having a water-gradient structural configuration, an increase from 33% to over 80% water content from core to surface. This unique design delivers a highly-lubricious and extremely-soft lens surface. Such soft contact lenses can be produced according to a cost-effective approach that is described in U.S. Pat. No. 8,529,057 (herein incorporated by reference in its entirety) and involves a step of crosslinking and covalently attaching of a water-soluble highly-branched hydrophilic polymeric material onto lens surfaces to form surface gels.
According to U.S. Pat. No. 8,529,057, a water-soluble highly-branched hydrophilic polymeric material is prepared by partially reacting a polyamidoamine-epichlorohydrin (PAE) with a wetting agent, at various concentration ratio of PAE to the wetting agent and at a reaction temperature for a given reaction time, to achieve a desired lubricity of the surface gels while minimizing or eliminating surface defects (e.g., surface cracking, etc.). However, methods described in U.S. Pat. No. 8,529,057 may not be efficient, as it requires a relatively long reaction time (i.e., at a higher production cost) and/or a relatively-larger amount of a wetting agent. The relatively long reaction time and excessive amount of a wetting agent (especially a relatively expansive wetting agent) can increase the production cost.
Therefore, there is still a need for developing a cost-effective method for producing water-soluble highly-branched hydrophilic polymeric material useful for producing water gradient contact lenses.